胡萝卜热风干燥特性实验研究

对新鲜胡萝卜进行了热风干燥特性实验研究,测量了干燥过程中的温度、质量和尺寸随干燥时间的变化,分析了干基含水率和温度随时间的干燥特性曲线。研究结果表明：胡萝卜干燥过程大致可以分为三个阶段，恒速干燥期、第一降速期和第二降速期；胡萝卜干燥过程物理尺寸保留率与干基含水率较符合二次多项式关系；在本实验条件范围内热风温度、速度和相对湿度对胡萝卜干燥速率具有一定的影响：温度越高、风速越大、相对湿度越小,干燥速率越大。     

生物质流化床热风干燥特性研究

在一个自制的能实时检测质量的流化床干燥试验装置上对一种速生林木材的热风干燥特性进行了深入系统的研究,分析了热风温度、热风速度以及料层高度等对生物质样品干燥热特性的影响。结果表明:干燥速率随温度和风速的增加而增大;随料层厚度的增加而下降;物料的含水率越高,干燥速率越快,随含水率的变化,各条件对干燥速率的影响程度发生改变。通过对干燥过程模拟分析发现,干燥曲线以及脱水速率分别符合薄层Page模型和线性方程模型,且干燥方程中的参数k主要受风温和料层厚度影响,参数n则主要受风速影响。     

不同孔隙率下加气混凝土吸放湿性能试验研究

为研究孔隙率对加气混凝土中湿分迁移特性的影响,采用恒温恒湿箱控制环境相对湿度和温度的方法对具有三种不同孔隙率的加气混凝土试样的动态吸湿和放湿过程进行了测试。研究结果表明,在等温吸湿过程中,加气混凝土试样的孔隙率越大,其含水率增长速率越大且平衡含水率也越高;而在等温放湿过程中,孔隙率越大的试样含水率下降速率越快且平衡含水率也越小,达到放湿平衡所需的时间则随相对湿度的提高而增长。比较不同环境温度下的吸放湿过程可知,较低的环境温度使得试样达到平衡状态所需的时间显著增加。此外,根据等温吸湿数据给出了加气混凝土吸湿平衡含水率随相对湿度变化的分段函数拟合公式。     

燃气轮机进气管道内喷雾蒸发冷却数值模拟

为了研究燃气轮机进气空气状态对其管道内液滴汽化长度的影响,采用DPM模型方法从进气温度、相对湿度、进气速度3方面对进气管道内喷雾直接蒸发冷却进行数值模拟和分析。模拟结果表明:进口空气温度越高,相对湿度越大,液滴在管道内汽化长度越短;适当地降低进口风速有利于降低液滴的汽化长度;雾化液滴的直径越小液滴汽化距离越短。     

垃圾焚烧炉干燥床垃圾干燥过程研究和分析

对部分垃圾组分进行了恒温条件下干燥失重情况的试验研究,同时通过理论分析和计算,研究了炉排.循环流化床复合垃圾焚烧炉干燥床上垃圾的干燥过程.结果表明:垃圾干燥过程中,干燥温度越高,失重率越大,但垃圾失重率并不是温度的简单线性函数;不同种类垃圾的干燥效果受其原始含水率和自身结构的影响,干燥过程有显著差异;比表面积越小的垃圾越难干燥;干燥床与辐射窗的比例在1和1.2之间,干燥床的适宜倾角为20°～30°,辐射角系数O.5-0.6;实际干燥床上的垃圾受炉膛辐射、干燥风对流和垃圾自身局部燃烧等综合因素影响,可使垃圾表层的水分蒸发率达40%左右.     

湿热地区波纹翅片管式表冷器的运行性能和调节能力研究

表冷器作为空调系统中空气的热湿处理设备在湿热地区应用广泛。然而,随着户式中央空调的发展,它与中小型冷水机的匹配及运行优化仍缺少指南。建立了某9排管空气-水逆流式波纹翅片管式表冷器的传热除湿数学模型。模拟结果分析表明:室外气象参数的影响显著,气温越高且露点温度越高,则其供冷和除湿能力显著提高;在广州和杭州六月份平均气象条件下,调节表冷器的供水温度、供水流速或管外风速,其供冷能力可分别在名义供冷能力的32%~95%以及45%~120%内调节,除湿能力也可相应随之得到调节;入口水温愈低,则变水量或变风量对表冷器供冷及除湿能力的调节作用范围越广;风速愈大且水流速度愈高,则变水温的调节作用范围越广;入口水温越低、风速越大或水流速度越大,则联合调节风量水量、水温水量或水温风量对其供冷和除湿能力的调节作用范围也越广。     

高水分毛竹废弃物非等温干燥特性及其动力学

文章基于热重分析对高水分毛竹废弃物的非等温干燥特性进行了研究,探讨了含水率和升温速率对毛竹废弃物干燥过程的影响。研究结果表明:含水率越高,升温速率越小,干燥所需的时间越长。采用迭代法对水分比以及4种非等温干燥模型进行非线性回归拟合分析,通过综合分析评价参数和残差分布可知,Henderson模型具有较好的拟合效果,是描述毛竹废弃物内部水分迁移规律的最优模型,并得到毛竹废弃物干燥所需的表观活化能为34.35～41.75 kJ/mol。     

生物质干燥及成型过程挥发性有机化合物(VOC)释放特性的研究

研究了生物质干燥及成型过程中VOC的释放量及释放比例,通过对4家企业干湿原料及产品中VOC含量的分析,考察干燥介质、停留时间和进口温度、干燥后含水率及成型过程等对VOC排放的影响。在考察的几个因素中,以停留时间对VOC释放量的影响最大,停留时间越长,VOC释放量及释放比例越高,同时几个因素又相互制约影响。研究表明,VOC的释放以干燥阶段为主,一般占到总释放量的70%以上,因此,控制干燥阶段的相关参数是减少VOC释放的主要手段。成型阶段VOC的释放主要和原料含水率有关,含水率越高,成型过程VOC释放量也就越高。     

密实度及有荷干湿循环对土-水特征曲线的影响

鉴于土-水特征曲线在非饱和土的研究中具有重要意义,采用Tempe压力膜仪和多功能土-水特征曲线试验仪,研究了密实度及固结压力下干湿循环对非饱和重塑粘土的土-水特征曲线的影响,并利用Van Genuchten模型对试验结果进行曲线拟合。结果表明,土体密实度越大,所受固结压力越大,则土体的进气值越大,失水速率越小,残余含水率越大;在固结压力下的干湿循环过程中,脱湿曲线失水速率越小,进气值越大,随干湿循环次数的增多,因土体孔隙发生改变,脱湿曲线的进气值呈增大趋势,且回滞环逐渐减小。     

综合管廊断面和风速对排烟影响的数值模拟研究

应用火灾模拟软件PyroSim,对综合管廊电缆舱火灾进行数值模拟,讨论不同断面高宽比和风速对排烟效果的影响。分析得到:排烟过程中,下部区域排烟效率高于上部区域;同一断面下,风速越小排烟效率越低;高宽比对于排烟效率影响较大,风速相同时,高宽比越大,下部排烟效率越高,而上部排烟效率越低,高宽比越小,其整体排烟效率越高。     

基于CFD技术的太阳能污泥干燥室内热湿环境研究

基于传热传质理论,建立一种太阳能污泥干燥室内热湿耦合传递的数学模型。综合考虑空气流动以及对流和辐射传热,利用CFD软件Fluent的k~ε湍流模型、组分输运模型及辐射模型,初步分析了在太阳辐射条件下不同干燥室结构、排风形式以及通风量对太阳能污泥干燥室内干燥区域的温度、相对湿度以及速度分布的影响。模拟结果表明:干燥室内温、湿度模拟值与实测值吻合较好,平均相对误差分别为3.55%和5.39%。对比分析不同结构下干燥室内的流场分布,两出口排风形式的太阳能污泥干燥室可以形成良好的干燥微环境。当两出口排风风速≥5 m/s时,室内干燥区域温度高于室外环境温度,同时相对湿度低于室外环境相对湿度,且增大出流风速,在干燥区域内空气扰流强度增强,有利于干燥室内污泥水分的蒸发。     

Performance studies of solar tunnel dryer for drying aonla (embilica officinalis) pulp

A solar tunnel dyer was constructed and evaluated the performance for drying aonla pulp. The dryer consists of a transparent UV stabilized plastic covered solar collector cum drying unit. Evaluation parameters are air temperature, solar insolation, moisture content, relative humidity and airflow rate. A minimum of 111.18 m² solar collector area is required to dry a batch 1000 kg aonla pulp in 16 hours (two days drying period). The initial and final moisture content considered were 424.93 and 10.08% dry basis, respectively. It was observed that on an average 43 per cent of higher temperature was obtained in solar tunnel dryer over the ambient temperature. The results obtained during the test period denoted that the maximum gained energy occurred at 13 o’clock hour and then gradually declined since the maximum solar radiation occurred at this time.     

An Investigation on the performance Improvement of greenhouse-type agricultural dryers

Drying is simply the process of moisture removal from a product. It can be performed by various methods. In these methods, thermal drying is most commonly used for drying agricultural products. These drying systems are usually classified into low and high temperature dryers according to their operating temperature ranges. In low temperature drying systems, natural-circulation greenhouse-type dryers appear the most attractive option for use in rural locations. They are superior operationally and competitive economically to natural open sun drying. Therefore, two different types of natural-circulation greenhouse crop dryers were designed, constructed and tested for their performance in this investigation. Each dryer mainly consisted of a framework constructed from black coated metal bars, corrosion-resistant plastic mesh and a black coated solar radiation absorber surface. The frameworks of the dryers were clad with clear polyethlene sheet on the all sides. The cladding at rear side was arranged to allow put the moist products into the drying chamber or get dried product from there. The clear plastic cladding at the bottom edge of the front side and rear side was also arranged to allow air to flow into the chamber, while the rectangular stream at the top of the end served as the exit for the moist exhaust air. The dryers were tested in the summer conditions. They were aligned lengthwise in the north-south axis during experiments. All dryers were experimented without crops (no product loaded) and with crops (pepper loaded). The dryers were also tested with chimney constructed from a galvanised iron sheet and without chimney in order to determine the effect of the chimney on the air flows. In addition, pepper was dried in the open-sun drying in order to compare the greenhouse dryers with open air drying. During experiments, temperature distribution inside drying chamber, pepper surface temperature, moist exaust air velocity, wind velocity, solar radiation, temperature and relative humidity of the atmosphere air were measured. Pepper samples, collected from open sun dryer and different positions in greenhouse dryers were also weighted to note amount of water evaporated. The results of the study show that the use of natural-circulation greenhouse dryers for drying agricultural products, is 2…5 times more efficient than open air drying and using black coated solar radiation absorber surface and chimney improve the performance of these dryers. Besides, the output of the greenhouse type dryers has also high quality, compared with open air drying.     

Thermal analysis in fluidized bed drying of moist particles

This paper deals with thermal modeling of the fluidized bed drying of wet particles to study heat and mass transfer aspects and drying thermal efficiencies. The model is then validated with the literature experimental data obtained for corn. A parametric investigation is undertaken to study the effects of the inlet air temperature, the air velocity and the initial moisture content of the material (i.e. corn) on the process thermal efficiency. The results show that the thermal efficiencies of the fluidized bed drying decrease sharply with decreasing moisture content of corn and hence increasing drying time, and apparently become the lowest at the end of the drying process. This clearly indicates that the moisture transfer from the material depends strongly on the air temperature, air velocity and the moisture content of material. A good agreement is obtained between the model predictions and the available experimental results.     

Development of design charts for tunnel dryers

A dryer simulation model, comprising a material model and an equipment model, has been developed for the drying of food products in a tunnel dryer. The material model, which deals with the drying kinetics of the product, is based on the receding evaporation front phenomenon while the equipment model describes the dynamics of the dryer. The overall model takes into account the shrinkage of the product. Simulation results of the transient moisture content show good agreement with experimental results for two dryers of different drying capacity. We present a design chart relating air temperature and humidity to the required energy for drying and dryer length, which shows an appreciable effect of setting low humidity for low temperature drying. A reduction in dryer energy consumption and chamber size is obtained under this condition. Multi-stage drying is introduced for situations where saturation of the air is likely to occur in the drying chamber. © 1997 by John Wiley & Sons, Ltd.     

Influence of process control strategies on drying kinetics,colour and shrinkage of air dried apples

The influence of two different control strategies, constant air temperature and constant product temperature, on product quality and drying behaviour of apples was investigated. The interactions of the drying parameters air temperature (35–100 °C), product temperature (35–85 °C), dew point temperature (5–30 °C) and air velocity (2.0–4.8 m/s) with drying time, colour changes and shrinkage were measured continuously and determined for both strategies. Based on these results the two strategies were compared with regards to their effect on drying performance.The results show that the drying strategy has a significant influence not only on the development and duration of the drying process but also on the development of colour changes and shrinkage. Controlling product temperature led to shorter drying times and generally lower colour changes. Furthermore, it was shown that the product temperature develops characteristically; two stages and a clearly visible transition period can be detected. This potentially can be used to control the process and, therefore, improve its performance regarding duration and quality aspects.     

Studies on thin layer drying of bagasse

Thin layer drying experiments of bagasse were carried out to determine the drying kinetics and also to identify a suitable drying model. The drying experiments were conducted in a laboratory scale dryer for a wide range of air temperatures (80–120°C), velocities (0.5–2 m/s), humidity level of air (9–24 g water(kg of d.a)⁻¹) and product thickness (20–60 mm). Air temperature, velocity, humidity and mass of product were recorded continuously during experimentation. The data were fitted to the different semi-theoretical or empirical models and compared based on their correlation coefficient (r), chi-square (χ²), root mean square error and mean bias error values. Among the models considered, the Page model gave accurate predictions with a correlation coefficient of 0.99627. It is found that the drying of bagasse takes place only in the falling rate period, even though the product has high initial moisture content. Copyright © 2006 John Wiley & Sons, Ltd.     

置换干燥原理及其在木材干燥中的应用

置换干燥是利用某种置换剂来置换湿物料中水分的一种非热力干燥方法。其干燥机理有两种形式 :“卷起 -浮升”机制和“颈缩”机制 ,主要特点为能量消耗低、干燥效率高、干燥时间短 ,且在被干燥物料表面不留水分斑迹。置换干燥在电子、航天、机械等方面已得到广泛应用。利用置换干燥方法干燥木材具有很强的吸引力和广阔的应用前景。为了降低木材干燥过程的能量消耗 ,提高出材率和产品质量 ,对不同的需干燥的木材应确定合理的干燥时间 ,选择合适的置换剂 ,并采取多级萃取的逆流结构。